Implementation example of C++ traversal map

In C++,std::mapIt is an associated container that stores key-value pairs and sorts the keys in the order of the keys. Traversalstd::mapThere are many ways, and the following are several common ways:

1. Use range for loop (C++11 and above)

Range-based for loop is a simple way to traverse containers introduced by C++11.

#include <iostream>
#include <map>

int main() {
    std::map<int, std::string> myMap = {{1, "one"}, {2, "two"}, {3, "three"}};

    for (const auto& pair : myMap) {
        std::cout << "Key: " <<  << ", Value: " <<  << std::endl;
    }

    return 0;
}

In this example,pairis a key and valuestd::pairObject,It's the key,is value.

2. Use the iterator

Iterators are the traditional way to traverse STL containers.

#include <iostream>
#include <map>

int main() {
    std::map<int, std::string> myMap = {{1, "one"}, {2, "two"}, {3, "three"}};

    for (auto it = (); it != (); ++it) {
        std::cout << "Key: " << it->first << ", Value: " << it->second << std::endl;
    }

    return 0;
}

In this example,itis an iterator pointing tostd::mapelements in  .it->firstandit->secondAccess keys and values ​​separately.

3. Use a reverse iterator

If you want tostd::mapThe end of   starts traversal, and you can use a reverse iterator.

#include <iostream>
#include <map>

int main() {
    std::map<int, std::string> myMap = {{1, "one"}, {2, "two"}, {3, "three"}};

    for (auto it = (); it != (); ++it) {
        std::cout << "Key: " << it->first << ", Value: " << it->second << std::endl;
    }

    return 0;
}

Reverse iterators work similarly to forward iterators, but they start at the end of the container and move forward.

Things to note

• During the traversal, do not modify the size of the container (for example, do not insert or delete elements), as this may cause the iterator to fail.
• If you only need to iterate over keys or values, not key-value pairs, you can usestd::map::keys()orstd::map::values()(C++20 and above) to get the views of keys or values ​​and iterate over them. However, please note that these methods are not available in pre-C++20 standards.

Which traversal method to choose depends on your specific needs and the C++ standard version. Range for loops are usually the cleanest and modern way, but iterators offer more flexibility and control.

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